An integrated research program is planned to investigate the relationship of malignancy and differentiation and the functions of the protease plasminogen activator (PA) in normal neural development and in the malignant phenotype. Primary neural cultures and malignat neuroblastoma cell lines will be studied. PA has been suggested to be involved in both normal cell migrations and malignant invasiveness. In order to evaluate these postulated roles, we need to know more about how PA is released from cells and localized to extracellular sites. The proposed work will characterize a form of PA which malignant, (and possibly some normal) cells can deposit on the substratum. This protease could function in localized cell surface and extracellular matrix molecule modifications involved in cell locomotion. In particular a role in neurite extension will be evaluated. To understand the function of PA in normal cells, it is important to know the range and common characteristics of cells secreting this enzyme. Our previous study showed that granule neurons in developing cerebellum secrete PA and the proposed work will extend these studies to examine other neuron and glial cell types in the developing nervous system. Experimental systems in which malignant cells can be differentiated to a normal phenotype provide information on the nature of malignancy as well as opportunities to study development with clonal cell populations. The proposed studies on neuroblastoma differentiation in synthetic media are direted at: identifying molecules mediating proliferation or differentiation; understanding the effects of cyclic nucleotides on neuronal differentiation and survival; and learning more about the commitment phase of cell differentiation. A study of tumor promoting phorbol esters on neural gene expression will likewise serve as a probe of discrete events (proliferation, morphology changes, and enzymatic maturation) in glial differentiation and identification of specific stages at which tumor promoters may act.